Carburetor



Feb. 15, 1966 C. L. MARTIN ETAL CARBURETOR Filed May 13, 1963 INVENTOR.CHARLES MARTIN BJOEL. B. JOH ON AGENT United States Patent N.Y., acorporation of New Jersey Filed May 13, 1963, Ser. No. 279,716 6 Claims.(Cl. 261-969) This invention relates to carburetors, and moreparticularly to carburetors of the class having a diaphragm for controlof fuel admission thereto.

The invention is especially concerned with carburetors of the classdescribed for small internal combustion engines, such as are used onpower saws, for example, he e b ity to p rat n any p sitio even p iddown, is important. For such application, fiat-type carburetors aregenerally unsuitable, and a diaphragm-type carburetor is preferred. Atypical diaphragm-type carr w h s a fu cha be cl se by a d ap a which issubject on the outside to atmospheric pressure. The diaphragm actuates avalve controlling admission of fuel to the fuel chamber from a fuelsupply tank. Fuel is adapted to be u plied from the fuel chamber to themixture conduit of the carburetor via a so-called high-speed fuel systemby pressure of the diaphragm on the fuel in the fuel chamber, resultingfrom vacuum drawn in the mixture conduit on operation of the engine.

In such a carburetor, the fuel chamber acts in effect as a sensingchamber, sensing the demand for fuel as reflected by the position of thethrottle valve of the carburetor. The sensing function of the fuelchamber is generally based on what may be termed a solid fuel conditionin-the chamber, meaning a condition in which the chamber issubstantially free of bubbles of air or fuel vapor. Accuracy of sensingis adversely affected by the presence of such bubbles in the chamber,noting that such bubbles are compressible whereas liquid fuel withoutbubbles therein (which may be referred to as solid fuel) is notcompressible. should be a substantial accumulation of bubbles in thefuel in the fuel chamber, pressure of the diaphragm on the fuel andbubbles in the chamber may initially rcsult merely in compression of thebubbles without delivery of fuel to the mixture conduit in the amount ofdemand. This results undesirably in lag of delivery of fuel. Air mayenter the fuel chamber due to what may be referred to as back bleeding,resulting from fuel being pulled out of the high speed system on accountof suction from the idle system of the carburetor, with resultantdiminution of fuel in the high-speed system and entry of air to replacethe lost fuel. This results in fuel being taken. away from the nozzle ofthe highspeed system with the result that when the throttle is openedfor acceleration from idle, there may be a lag in delivery of fuel tothe nozzle.

Accordingly, among the several objects of the invention may be noted theprovision of a carburetor of the class described which is so constructedthat bubbles of air and fuel vapor are purged from the fuel chamber tomaintain a better solid fuel condition in the fuel chamber for moreaccurate sensingof fuel demand, and also so that back bleeding isminimized, thereby providing for more accurate sensing of fuel demandand tending to avoid lag in delivery of fuel to the mixture conduit ofthe carburetor on acceleration; and the provision of a carburetor suchas described which is economical to manufacture and reliable inoperation even in extreme positions, including upside down position. Ingeneral, the stated objects are accomplished by a special formation ofthe fuel chamber of the carburetor and by special passage meansextending from the fuel chamber to the For example, if there mixtureconduit for purging the chamber. Other objects and features will be inpart apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafterdescribed, the scope of the invention being indicated in the followingclaims.

In the accompanying drawings, in which several of various possibleembodiments of the invention are illustrated,

FIG. 1 is a longitudinal section of a diaphragm-type carburetorconstructed in accordance with this invention;

FIG. 2 is a traverse section taken generally on line 22 of FIG. 1,showing the high-speed fuel system of the carburetor, a fuel tank and aline from the tank to the carburetor being illustrated diagrammatically;

FIG. 3 is a fragmentary section of the carburetor shown in FIG. 1, takengenerally on line 3-3 of FIG. 1;

FIG. 4 is a fragmentary section of a modified version of the carburetortaken generally on the same line as FIG. 1;

FIG. 5 is a view similar to FIG. 4 illustrating another version of thecarburetor; and

FIG. 6 is a fragmentary section of a third modified version of thecarburetor taken on the same line as FIG. 2.

Corresponding reference characters indicate corresponding partsthroughout at the several views of the drawings.

Referring to the drawings, a carburetor constructed in accordance withthis invention, and generally designated 1, is shown to comprise a mainbody 3 formed to provide a mixture conduit 5 extending thercthrough fromone end to the other. As appears in FIG. 1, the mixture conduit 5 isformed to form a cylindric throttle bore 7 toward one end, anintermediate venturi section 9, and an inlet section 11 toward its otherend. The latter is generally cylindric, but with a flat as indicated at13. The throat (the region of smallest cross section) of the venturi isindicated at 15. Body 3 has a flange 17 at the said one end of themixture conduit (which con stitutes its downstream end) for attachingthe carburetor to the intake manifold 19 of an internal combustionengine as appears in FIG. 1, the flange being provided with suitablebolt holes (not shown) for receiving bolts extending from the intakemanifold for this purpose.

An air filter 21 is attached in suitable manner to the body 3 at theupstream end of the mixture conduit. As appears in FIG. 1, this airfilter is of a type comprising a casing 23 containing an annular filterelement 25. The hole in the center of the filter element is indicated at27. This hole is aligned with the mixture conduit 5. Air enters thefilter peripherally, flows through the filter element to the hole 27,and thence through the mixture conduit during the operation of theengine.

Body 3 is formed with a recess 29 of circular outline in one sidethereof (its bottom side as appears in the drawings). This recess, whichconstitutes a fuel chamber, is generally dome-shaped. Body 3 has aportion 30 extending down and from one side of the recess into thecenter of the recess. The center of the recess is generally in the planeof the venturi throat 15. The fuel chamber is closed by a flexiblediaphragm 3*]. (made of fuel-resistant synthetic rubber, for example).The margin of the diaphragm 31 is clamped against the body by a cover33, fastened to the body by screws as indicated at 35. Cover 33 isrecessed as indicated at 37 and has a vent hole 38. A gasket 39 isinterposed between the margin of the diaphragm and the cover. Thecentral portion of the diaphragm is maintained substantially flat andrigid by a pair of flat spoked wheel-like backing member 41 and 43 lyingon opposite faces of the diaphragm, and held in as sembly with thediaphragm by a rivet 45 having its shank extending through a center holein the diaphragm and center holes in members 41 and 43. The inner endhead of the rivet is in the form of a button 47 for engagement by oneend of a valve-actuating lever 49.

Fuel is adapted to be supplied to fuel chamber 29 from a fuel tank T,the carburetor including fuel pump means as generally indicated at 53for pumping fuel to chamber 29, and a needle valve 55 controlled by theaforementioned lever 49 for controlling delivery of fuel to the fuelchamber 29. For purposes of providing the fuel pump means, body 3 isformed with a shallow circular recess 57 constituting a pulsationchamber in the side thereof (its top side as shown) opposite the chamber29 and, laterally offset from this recess 57, with an annular cavity 59surrounding a boss 61. Recess 57 and cavity 59 are closed by a flexiblepump diaphragm 63 (made of fuel-resistant synthetic rubber, for example)clamped against the body all around the recess 57 and the cavity 59 by apump cap 65. The latter is fastened to the body by screws as indicatedat 67. It has a recess 69 constituting a pumping chamber on the oppositeside of the diaphragm from recess or pulsation chamber 57.

The pump cap is formed with an upwardly extending boss 71 having ahorizontal hole 73 extending inward from one side of the carburetor anda vetrical hole 75 extending down from the inner end of hole 73 to thepumping chamber 69. Holes 73 and 75 together constitute a fuel inletpassage. A nipple 77 pressed in the end of hole 73 is adapted forconnection of a fuel line 78 leading from the fuel tank T. The pump capis also formed with an outlet dome 79 which opens upward from pumpingchamber 57 alongside hole 73, from which there is an inclined outletpassage 81 to a cavity 83 in the pump cap on the opposite side of pumpdiaphragm 63 from the annular cavity 59. From the pulsation chamber 57there is a passage 85 through the body 3 of the carburetor forcommunication between the intake manifold 19 and pulsation chamber 57.Pressure pulsations such as occur in the intake manifold (as in the caseof a two-cycle engine, for example) are transmitted through passage 35to chamber 57 and cause flexing of pump diaphragm 63. Fuel is therebydrawn into pumping chamber 69 from tank 51 through inlet passage 73, 75on downstrokes of diaphragm 63 and forced out of pumping chamber 69 onupstrokes of the diaphragm 63 through outlet chamber 79 and outletpassage 81 under control of flapper-type inlet and outlet check valves87 and 89. These are formed by C-shaped cuts in a valve memberconsisting of a disk 91 of fuel-resistant synthetic rubber, for example,held in place by a retainer 93. The inlet flapper valve 87 flexes downto open when diaphragm 63 flexes down (outlet check 89 then beingclosed), and flexes up to close off the lower end of hole 75 whendiaphragm 63 flexes up. The outlet flapper valve 89 flexes up to openwhen diaphragm 63 flexes up (inlet check 87 then being closed) andflexes down to close off an outlet hole 94 in retainer 93 when diaphragm63 flexes down.

Body 3 has a cylindric pocket 95 extending up from fuel chamber 29alongside the mixture conduit 5, this pocket being aligned with theaforementioned boss 61. A passage 97 extends down through the boss 61and the body 3 to the upper end of the recess 95. A flanged tubularfitting 96 pressed in the upper end of passage 97 holds down the pumpdiaphragm 63. A tubular cylindric needle valve body 99 is received inrecess 95, being held in recess 95 by a screw-threaded fitting 101threaded in the lower end of this recess. The needle valve body 99 hasan upper end head 103 provided with an axial bore 105 forming acontinuation of passage 97. A resilient valve seat 107, consisting of adisk of fuel-resistant synthetic rubber, for example, having a centerhole, is retained at the bottom of the head 103 as by a ring 109 pressedinto the needle valve body. The latter has a reduced extension 111 fromthe upper end of head 93 having an annular groove receiving an O-ring113 for sealing against body 3 at the upper end of recess 95.

Fitting 101 has a central opening slidably receiving the stem of needlevalve 55, the latter having a tapered nose 115 at its upper end forengagement with valve seat 107. The opening in the fitting is formed forflow of fuel therethrough around the stem of the needle valve. A coilcompression spring 117 surrounding the needle valve reacts from thelower end of retainer 101 against a collar 119 on the needle valve tobias the needle valve to a closed position engaging the valve seat 107.The needle valve has an annular groove 121 at its lower end providing alower end head 123 on the needle valve. The valve-actuating lever 49comprises a metal strip bent as indicated at 125m form an upwardlyopening loop. Lever 49 is pivoted intermediate its ends on a pivot pin127 received in loop 125. This pin extends parallel to the axis of themixture conduit 5 across the upper portion of the fuel chamber 29. Lever49 thus extends laterally in respect to the carburetor and has its innerend overlying button 47 on the control diaphragm 31. The outer end ofthe lever is forked as indicated at 129 and straddles the needle valve55 within the groove 121 above the lower end head 123 of the needlevalve.

A throttle shaft 131 is journalled in body 3 extending laterally acrossthrottle bore 7 of the mixture conduit 5. Shaft 131 carries a throttle133 constituted by an elliptical sheet metal plate, and has an operatingarm 135 on one end. A choke shaft 137 is journalled in body 3 extend=ing laterally across the inlet section 11 of mixture con duit 5. Shaft137 carries a choke 139 constituted by a sheet metal plate, and, as willbe understood, has an operating arm (not shown) on one end.

Body 3 is formed with a hole 141 extending up from the center of fuelchamber 29 through the projection 30 to mixture conduit 5, this holebeing closed at its lower end by plug 143. Hole 141 is stepped, havingan enlarged portion 147 forming a fuel well and a smaller upper por=tion 149. A nozzle 151 is received in the hole 141. This nozzlecomprises a tubular element with an upper portion having an outsidediameter corresponding to the diameter of the upper portion 149 of hole141, and a lower portion having a diameter corresponding to the lowerportion 147 of hole 141. The tubular element is pressed into the hole.The lower end of the nozzle extends into the fuel well 147 and the topof the nozzle extends up into the venturi throat 15.

Body 3 is provided with a tubular extension 152 ex= tending down fromthe body alongside hole 141 (on the side thereof opposite the needlevalve pocket 95) to a point between lever 49 and diaphragm 31. Thetubular extension 152 and body 3 have a common cavity 153' extending upfrom the fuel chamber 29. It will be seen that cavity 153 opens into thefuel chamber in close proximity to diaphragm 31. Cavity 153 isintersected by a lateral horizontal hole 155 which at its inner end isin communication with the fuel well 147 via an orifice 157. The upperportion of the nozzle has ports 159, the purpose of which will becomeapparent hereinafter, and the lower portion of the nozzle is open a itslower end 161 for communication from the fuel well 147 to the interiorof the nozzle. Cavity 153, hole 155, orifice 157, fuel well 147, and thepassage in nozzle 151 constitute the high-speed fuel circuit or systemof the carburetor, fuel being adapted to flow therethrough from chamber29 to the mixture conduit upon opening throttle 133 and resultant flowof air through the mixture conduit. The flow is adapted to be metered bya high speed system adjusting screw 163 threaded in hole 155 and havinga small diameter pointedend extension 165 reaching to the orifice 157.

In accordance with this invention, body 3 is formed with a small bleedpassage 167 extending from the upper part of the dome-shaped chamber 29to the upper part of the fuel well 147. Air and fuel vapor are adaptedto escape through bleed 167 from dome-shaped fuel chamber 29 to thespace around nozzle 151 at the upper part of hole 141, and thence passthrough ports 159 and out of the nozzle 151 into the mixture conduit.

Downstream from hole 141, body 3 has a cavity 171 (see FIGS. 1 and 3) inthe central longitudinal plane of the mixture conduit 5 extending upfrom fuel chamber 29 An idle port 173 opens from the upper end of thiscavity into the mixture conduit 5 downstream from the closed throttle133. An idle air bleed hole 175 opens into the upper end of this cavityfrom mixture conduit 5 upstream of the closed throttle. The lower end ofcavity 171 is closed by a plug 177. Body 3 has a downwardly extendingtubular projection 178 extending down into the fuel chamber alongsidecavity 171 to a point adjacent diaphram 31. The downwardly extendingprojection 178 and body 3 form a cavity 179 extending up from the fuelchamber 29. It will be seen that cavity 179 opens into the fuel chamberin close proximity to diaphragm 31. Cavity 179 is intersected by alateral horizontal hole 181 which at its inner end is in communicationwith cavity 171 via an orifice 183. Cavity 179, hole 181, orifice 183,cavity 171 and port 173 constitute the low-speed or idle system of thecarburetor, fuel being adapted to flow therethrough from fuel chamber 29to the mixture conduit 5, and air mixing with the fuel via port 175. Theflow is adapted to be metered by an idle adjusting screw 185 threaded inhole 181 reaching to the orifice 133.

Operation is as follows:

On starting the engine (choke 139 set in starting position for limitedsupply of air to mixture conduit 5, and throttle 133 opened), fuel forstarting is delivered from fuel chamber 29 to mixture conduit 5 via thehigh-speed circuit, i.e., cavity 153, hole 155, orifice 157, fuel well147 and the passage in nozzle 151, and via the low-speed circuit, i.e.,cavity 179, hole 131, orifice 183, cavity 171 and ports 173 and 175. Thefuel mixes with air flowing through the mixture conduit. The largeamount of fuel delivered to the mixture conduit 5 through the high-speedand idle systems provides a relatively rich air/fuel mixture forstarting.

After the engine has started and warmed up, choke 139 may be fullyopened, and throttle 133 controlled as desired for high speed operation.As previously noted, intermediate section 9 of mixture conduit 5 isrestricted to provide a venturi effect such as to generate a partialvacuum in the mixture conduit in the region of high speed fuel nozzle151 to draw fuel out of chamber 29. Diaphragm 31 is subject on its outerside to atmospheric pressure through vent hole 33. As fuel is taken outof chamber 29, diaphragm 31 moves inwardly against the bias of spring117 to open the valve 55 through the action of lever 49. Fuel flows intochamber 29 to replace fuel leaving through nozzle 151.

It is to be noted that any air bubbles in the fuel in the fuel chamberwill rise into the upper dome portion of the chamber 29. Similarly, fuelvapor resulting from volatilization of fuel collects in the dome. Duringhigh speed engine operation with the throttle away from its closedposition, air pressure in the venturi throat is less than that inchamber 29, as described. Therefore, in accordance with this invention,air and vapor are forced through the bleed passage 167 and the holes 159in the nozzle 151 to be discharged into the mixture conduit with thefuel. Thus, the fuel chamber is purged of air and fuel vapor to maintaina better solid fuel condition in fuel chamber 29 During high speedoperation, after air and vapor are purged through passage 167, fuel fromchamber 29 will pass through passage 167 into the fuel well 147.

Also, in accordance with this invention, the lower extremities of thetubular projections 152 and 178 reach down well below the level of thefuel in the fuel chamber 29 so as to tend to prevent air and fuel vaporfrom being drawn directly into the tubular extensions from above thelevel of the fuel.

For engine idling, throttle 133 is returned to its FIG. 1 position. Apartial vacuum is drawn downstream from the throttle, and this induces aflow of fuel from fuel chamber 29 to mixture conduit 5 downstream fromthe throttle via cavity 179, hole 181, orifice 183, hole 171 and port173.

During idle operation, the air in mixture conduit 5 upstream of throttle133 is substantially atmospheric. The fuel pressure in chamber 29 issubatmospheric due to the manifold vacuum acting through the idlecircuit, Thus there is a pressure differential across the main fuelcircuit between nozzle 151 and chamber 29, which tends to bleed smallamounts of air into the chamber 29 during idle operation. This airpasses through nozzle 151 and the main fuel circuit into chamber 29. Theclose spacing between needle end and passage 157 minimizes this airflow. Air which thus bleeds into chamber 29 during idle will passupwardly in chamber 29 and collect in the upper pockets of the dome ofchamber 29.

During engine idle operation, air is prevented from bleeding intochamber 29 through passage 167, by forming passage 167 with a diameteraround 0.040 inch. With the passage 167 filled with fuel, capillaryaction of the fuel tends to seal passage 167 to block the flow of airinto chamber 29. However, at high speed engine operation, the pressuredrop across passage 167 is greater than during idle operation so thatthe capillary seal is broken for purging chamber 29, as described.

Thus, with the above described construction, bubbles of air and fuelvapor are purged from the fuel chamber 29 into the mixture conduit inthe region of nozzle 151 to maintain a better solid fuel condition inthe chamber and back bleeding is minimized for more accurate sensing offuel demand and so that lag in fuel delivery on acceleration is avoided.

FIG. 4 illustrates a modification which in all respects is the same asthe embodiment of the invention shown in FIGS, 1-3 except that chamber29 has a somewhat different shape, and the bleed specially designated167a extends from the upper portion of the dome-shaped chamber 29 to themixture conduit 5, opening into mixture conduit immediately upstream ofthe nozzle 151.

FIG. 5 illustrates another modification which is in all respects thesame as the embodiment of the invention shown in FIGS. l-3 except thatthe bleed specially designated 167!) extends from the upper portion ofthe domeshaped fuel chamber 29 to the mixture conduit 5 immediatelydownstream from the nozzle 151.

FIG. 6 illustrates another modification which is in all respects thesame as the embodiment of the invention shown in FIGS. 1-3 except thatthe bleed specially designated 167a extends from the upper portion ofthe domeshaped fuel chamber 29 to the mixture conduit 5 generally in thesame transverse plane as the nozzle 151 and alongside the nozzle.

In view of the above, it will be seen that thefr' several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. A carburetor having a mixture conduit, a fuel source, means defininga dome-shaped fuel chamber, a diaphragm closing the bottom of said fuelchamber and means for moving said diaphragm by differential pressure, afuel inlet delivering fuel from said source to said fuel chamber, meansincluding a valve for controlling said fuel inlet, means including alever controlled by movement of said diaphragm for sensing the fuelrequirements and controlling said inlet valve, means defining a highspeed fuel system for delivery of fuel from said fuel chamber to saidmixture conduit, said means defining said high speed system including atubular fuel inlet conduit extending downward from the means definingsaid dome-shaped fuel chamber and terminating at a level between saidlever and said diaphragm and a high speed fuel nozzle extending intosaid mixture conduit, means defining a passage connecting said tubularinlet conduit with said nozzle, and a bleed passageway having an openingimmediately adjacent said fuel nozzle at one end and opening into theuppermost portion of said dome-shaped fuel chamber at its other end forpurging air and vapor from said fuel chamber to maintain a solid fuelcondition therein for more accurate sensing of the fuel demand,

2. A carburetor as set forth in claim 1 wherein said high speed systemfurther comprises a fuel well in communication with said chamber, saidnozzle extends into said well, and said bleed opens into said well.

3. A carburetor as set forth in claim 1 wherein said bleed opens intosaid mixture conduit adjacent said nozzle.

4. A carburetor as set forth in claim 1 wherein said bleed opens intosaid mixture conduit generally in the transverse plane of the fuelnozzle. 1

5. A carburetor as set forth in claim 1 wherein said high-speed fuelsystem further comprises a hole forming a fuel well, said hole having anupper portion smaller in diameter than said fuel well, said nozzlehaving an upper portion extending through the upper portion of said holeand a lower portion of larger diameter than the upper portion of thenozzle and in engagement with the wall of the fuel well to close theupper portion of the fuel well, said nozzle having ports therein betweenthe upper portion of said hole and the lower portion of said nozzle,said bleed opening into the upper portion of said fuel well.

6. A carburetor as set forth in claim 1 wherein said high-speed fuelsystem further comprises a hole forming a fuel well, said hole having anupper portion smaller in diameter than said fuel Well, said nozzlehaving an upper portion extending through the upper portion of said holeand a lower portion of larger diameter than the upper portion of thenozzle and in engagement with the wall of the fuel well to close theupper portion of the fuel well, said nOZZle having ports therein betweenthe upper portion of said hole and the lower portion of said nozzle,

References Cited by the Examiner UNITED STATES PATENTS 2,724,585 11/1955 Armstrong 261--69 2,979,312 4/ 1961 Phillips.

2,984,465 5/1961 Hazzard.

3,090,608 5/ 1963 Phillips.

HARRY B. THORNTON, Primary Examinen RONALD R. WEAVER, Examiner.

1. A CARBURETOR HAVING A MIXTURE CONDUIT, A FUEL SOURCE, MEANS DEFININGA DOME-SHAPED FUEL CHAMBER, A DIAPHRAGM CLOSING THE BOTTOM OF SAID FUELCHAMBER AND MEANS FOR MOVING SAID DIAPHRAGM BY DIFFERENTIAL PRESSURE, AFUEL INLET DELIVERING FUEL FROM SAID SOURCE TO SAID FUEL CHAMBER, MEANSINCLUDING A VALVE FOR CONTROLLING SAID FUEL INLET, MEANS INCLUDING ALEVER CONTROLLED BY MOVEMENT OF SAID DIAPHRAGM FOR SENSING THE FUELREQUIREMENTS AND CONTROLLING SAID INLET VALVE, MEANS DEFINING A HIGHSPEED FUEL SYSTEM FOR DELIVERY OF FUEL FROM SAID FUEL CHAMBER TO SAIDMIXTURE CONDUIT, SAID MEANS DEFINING SAID HIGH SPEED SYSTEM INCLUDING ATUBULAR FUEL INLET CONDUIT EXTENDING DOWNWARD FROM THE MEANS DEFININGSAID DOME-SHAPED FUEL CHAMBER AND TERMINATING AT A LEVEL BETWEEN SAIDLEVER AND SAID DIAPHRAGM AND A HIGH SPEED FUEL NOZZLE EXTENDING INTOSAID MIXTURE CONDUIT, MEANS DEFINING A PASSAGE CONNECTING SAID TUBULARINLET CONDUIT WITH SAID NOZZLE, AND A BLEED PASSAGEWAY HAVING AN OPENINGIMMEDIATELY ADJACENT SAID FUEL NOZZLE AT ONE END AND OPENING INTO THEUPPERMOST PORTION OF SAID DOME-SHAPED FUEL CHAMBER AT ITS OTHER END FORPURGING AIR AND VAPOR FROM SAID FUEL CHAMBER TO MAINTAIN A SOLID FUELCONDITION THEREIN FOR MORE ACCURATE SENSING OF THE FUEL DEMAND.